Answer to Question #333624 in Inorganic Chemistry for nashitaa

Question

A buffer was prepared by mixing 1.00 mole of ammonia and 1.00 mole of

ammonium chloride to form an aqueous solution with a total volume of 1.00

liter. To 500 mL of this solution was added 30.0 mL of 1.00 M NaOH. What

is the pH of this solution?

Answer 1

Number of mol of NH₃ = 500/1000 = 0.5mol

Number of moles of NH₄Cl = 0.5 mol

Number of moles of NaOH = 30/1000 = 0.03mol

pK_a of NH₃ = 9.25 

pH = pK_a + log (NH₃/NH₄⁺)

= 0.5/0.5 = 1 

Log 1 = 0

pH = 9.25 - 0 = 9.25 

∆ pH = 9.25 - 4.6 = 4.65